There are dozens of film screen protectors designed for application to the S4 screen. These protect against minor scratches.
If you want a more premium film, you have several choices. A popular choice is the ZAGG invisibleSHIELD High Definition, described by ZAGG as the number one selling scratch protection available. It's a thin film that the company says "has its origins in the military, where it was used to protect high-speed helicopter blades from dust, dirt and debris." (They also say it's patented, but it's not; when I looked up the patent, I discovered that what's patented is the box the product comes in!) The company offers a free lifetime replacement warranty for the product - not surprisingly, since the company website has YouTube videos of an iPhone being hammered at, attacked with a drill and even having bricks drop on it, all without damage.
Another rugged film is the Amzer ShatterProof, which the company says is "Army-grade protection." I found that it resisted scratches, but that the film could be indented if you tried deliberately. I scratched gently with a box cutter and had no difficulty producing an indentation. The indentations did not "heal"; they remained. But, again, it required a deliberate attempt to produce this effect. It too comes with a lifetime replacement warranty.
A bargain-priced film, available in a 3-pack, is the Tech Armor HD Clear. It resisted scratches, but could be damaged with deliberate effort.
If you want a protector that's stronger - and smoother - than plastic films, you can go with one that's made of glass, such as the BodyGuardz Pure, made of "special chemically-tempered glass exceeding the hardness of steel." A company video shows someone hammering at the screen protector - while it's on an iPhone. The phone survived undamaged. I didn't try this test myself on the Pure or any of the other screen protectors, figuring that potentially destroying my phone fell in the category of "kids, don't try this at home."
I did, however, try hammering the Pure when it wasn't on the phone. It didn't break. If you do manage to ever damage the Pure (accidentally, one assumes), you can get a replacement for a small fee to cover shipping. (That's a replacement of the Pure, not of your phone!)
I like the Pure, especially since it's smoother than a plastic screen protector. That makes using the phone feel more natural and comfortable. However, the glass makes the phone a bit heavier. Also, although advertised as smudge proof, the Pure readily retained smudges.
The Pure is 0.4 mm thick - that's twice the thickness of the Amzer film, for example - and you'll want to determine whether it will be compatible with your case. The company has a short list of yea's and nays. I tested it with two representative cases that I reviewed, the plastic+silicon Seidio Active and the snap-on Musubo Chamfer and found no problem.
However, I found it difficult to attach the Pure correctly, which is of course a risk with any screen protector. The screen protector adheres very quickly and firmly. I followed the installation instructions, which involve using an included suction cup to hold the Pure as you apply it, but I ended up with the screen protector misaligned. I also had a few small bubbles that have refused to disappear (as well as some large ones that disappeared within a day). I might have had better luck attaching the protector using the "hinge method" instead.
The problem with misalignment is not only that it looks snarky, but also that the Pure has a cutout that gives very little clearance for the front camera. With the Pure misaligned, I found that light could flare across the edge of the cutout and into the lens of the front camera, which sometimes created artifacts akin to lens flare.
Luckily, it's easy to remove the Pure: you just slide your fingernail under the glass and work it around the edge. When enough of the adhesion has dissipated, you shove a piece of paper between the Pure and the screen and work at it. Within a minute or so, the screen protector is off. No residue remains, because the adhesion depends on a specially engineered surface rather than any kind of sticky glue.
You can then wash the Pure with soap and water and reapply. This time the adhesion is not instantaneous, so it's a little easier to position the screen protector. But I found that I ended up with many more bubbles, many of them presumably due to dust particles, but also including two large areas on the edge of the screen. These did not affect responsiveness to touch, however. Bottom line: if you mess up the application of the Pure, you'll have little trouble removing it, but don't count on being able to reuse it unless you're tolerant of bubbles and the like.
Another glass screen protector is the iloome ScreenMate. It's more tolerant of misalignment than the Pure, because (unlike the Pure) it doesn't have a cutout for the sensors and front camera. Instead, the sensors and front camera are covered by glass, which means it's particularly important that there not be a bubble or bit of dust in those locations. Curiously, the ScreenMate does not include an alcohol wipe for cleaning the screen before application of the protector.
At 0.26 mm, the ScreenMate is thinner than the Pure and scarcely thicker than a film protector such as the Amzer. That may make the ScreenMate compatible with more case designs than the Pure, though as noted above, I didn't find any problem using the Pure with two very common designs. In any event, when I hammered at the ScreenMate (while it was not on a phone), it didn't shatter. So 0.26 mm seems to be thick enough.
I also examined the Tech Armor Ballistic Glass protector. Curiously, this product is identical to the Pure: not only does the product have the same uniquely-shaped cutout for the sensors and front camera, in fact the packaging is identical: the construction of the box, the markings ("OPEN") on the plastic package insert, the inclusion of a suction cup, etc. In every respect, the Bodyguardz Pure and the TechArmor Ballistic Glass are the same product.
I asked representatives of both companies to explain this and ultimately was told that they both probably used the same Asian supplier. The reason I installed the Pure is simply that I received the product sample first. I believe that my comments on the Pure apply equally to the Ballistic Glass, and thus your experience with either product is likely to be the same. I have no opinion as to which product came first.
Another option is the Spigen Glas.tR Slim (0.4 mm thick, and with curved bevel edges to the glass to reduce chipping); it covers the front camera but not the sensors. However, the cutout is close to the sensors, meaning that proper alignment is important, although perhaps a little less so than for the BodyGuardz and Tech Armor products. The product also includes a plastic film protector for the back cover of the phone, which I suppose is useful if you don't have a case for it. Spigen also offers the Glas.t Slim (0.28 mm, and no curved bevel; not reviewed).
Finally, I checked out the XGear Sentinel. The shape is similar to the Spigen. Like the iloome, there is no alcohol wipe included with the product.
Adding a glass screen protector has an unavoidable side effect: the home button, which wasn't very prominent to begin with, is now slightly recessed. To rectify this, the products reviewed come with plastic jelly bean stick-on buttons in black and white (one of each is included; the Spigen product includes an orange one as well). One exception: XGear's product only includes one button, in black, but it's aluminum. In addition, Spigen offers aluminum buttons for separate purchase.
Truth to tell, other than the shape of the cutout and the type of home button stickon included (or not), all of these glass products are pretty similar. Whichever one you choose, I recommend using it with a case, to help protect the edge of the screen protector from chipping.
That's it for screen protectors. Look for my next installment, where I examine a Bluetooth speakers. Afterward will come video (such as how to connect your cellphone to a TV), external batteries, USB chargers, USB cables, Bluetooth keyboards and mice, cables, how to use your cellphone as a portable office, and miscellaneous accessories. You can find all this at http://www.huffingtonpost.com/jonathan-handel/.
REAL LIFE. REAL NEWS. REAL VOICES.
Help us tell more of the stories that matter from voices that too often remain unheard.